Electromagnetic energy, such as laser light, is used to perform various surgical procedures including the vaporization of hyperplastic prostate tissues, for example. One optical device that is used with other surgical tools to perform such medical procedures is a side fire optical fiber device, also known as a lateral delivery device.
Lateral delivery optical fiber devices are typically used to redirect delivered electromagnetic radiation in direction other than the fiber longitudinal axis: typically at an angle of 70-90 degrees off the axis. Conventional side fire optical devices operate between angles of approximately 70-80 degrees off axis, or more precisely, 74 to 76 degrees, by reflecting the electromagnetic radiation off of a beveled and optically flat and smooth surface that is machined and polished directly upon the transmitting optical fiber conduit, exploiting total reflection at or below the critical angle as described by Snell's Law. The refractive index conditions for total reflection are typically maintained by protecting the fiber bevel surface with a circumferential protective cap, typically made of fused quartz or fused silica. The redirected output laser light is transmitted through the outer diameter of the fiber itself and then through the cap wall to exit a transmitting surface on the protective cap to address the surgical site.
The maximum off-axis output angle of a conventional side fire fiber is a function of the fiber numerical aperture (NA) which, in turn, is selected for compatibility with the light source focal condition and wavelength, where the wavelength also affects the fiber NA. Lower NA fiber permits higher the off axis redirection angles without axial leakage, at least theoretically, and produces lower the divergence in the laterally redirected energy. Competing designs considerations exist for low NA fiber, e.g. very low NA (0.1) all silica fiber, also known as “ASF” or “silica-silica” fiber, is more sensitive to optical losses under stress than moderate NA fibers, e.g. 0.22 NA ASF, particularly in compression and bending, and producing the lower angle laser foci required to couple to low NA fiber typically increases the laser focus minimum spot diameter which, in turn, requires larger less flexible fiber.
Side fire fibers have been used in some spectroscopic and specialized laser ordinance ignition applications, e.g. laser-induced breakdown spectroscopy, but by far the most common applications of such devices is in surgery, where safety and efficacy considerations have supremacy. Many applications of side fire fibers favor smaller core fibers for the very attributes of optical fiber: flexibility in delivery of concentrated electromagnetic energy. Fiber raw material pricing scales exponentially with diameter, but the minimum fiber diameter that is practical for most surgical applications of side fire fibers is also a function of the laser's focal spot diameter and drift, which is a function of the laser wavelength, M2 beam quality and laser output stability. Some fiber stiffness may be desirable in some applications for compliant torque transfer and resistance to buckling in controlling the fiber positional and rotational orientation. The largest fused silica fibers with any real utility in surgery are approximately 1 mm in diameter. For the most commonly used, 0.22 NA fibers, this diameter includes the fluorine-doped silica cladding but not the polymer coatings; at this time, the most commercially successful side fire fiber for prostate (BPH) surgery has a 0.75 mm core while competing BPH fibers are 0.6 mm core and 0.55 mm core.
Another design consideration for side fire fibers is the maximum off-axis angle that the light may be reflected for a particular fiber choice. Higher angles produce rounder spots (up to 90 degrees with respect to the fiber longitudinal axis), with higher energy density at the transmitting surface, generally, and typically less scattering of the redirecting light. Using Snell's law to calculate the critical angle for a ray that is parallel to the fiber longitudinal axis (at 587.6 nm, for reference, where the refractive indices for fused silica and air are 1.4585 and 1.0003, respectively) yields 43.3 degrees. In the convention of the art, the angle of the polished fiber surface is defined as the complementary angle to the critical angle for convenience of a direct relation to the fiber longitudinal axis, or in this case, 46.7 degrees off-axis. Producing such a polished surface on any fiber would offset the ray that is parallel to the fiber axis by 93.4 degrees—or 3.4 degrees beyond orthogonal—implying that a 90 degree side fire fiber is simple to produce; this result is illusive.
Some light within an optical fiber may be propagated parallel to the fiber axis—light referred to as the “0th order mode” when it is also on the axis—but these rays are not representative of light within the fiber, if they exist at all. Surgical lasers generally couple to fibers by way of a single lens, focusing a much larger beam (e.g. 5 mm) onto the smaller fiber. In determining the focal length of the fiber coupling lens, laser designers usually anticipate the lowest possible NA fiber that will find utility in combination with the laser to select a lens where the highest focal angle is less than the maximum acceptance angle for the fiber—how much less depends upon the designer and the assumptions used—with the goal of insuring the fiber acceptance cone cannot be overfilled. Where the laser designer considers minimum NA for the safety, the fiber designer must consider the maximum NA in side fire fiber design, even where the laser focus condition theoretically under fills the fiber NA. Fiber bending stresses between the laser and the side fire tip may convert lower angle light (or lower order modes) to higher angles, completely filling the fiber NA at the working tip of the fiber.
For 0.22 NA, barring special order, the maximum NA is 0.24 (0.22±0.02). The maximum angle for light propagated within this fiber is just under 9.6 degrees (arcsin NA divided by the fiber core refractive index), so the maximum angle that the fiber tip may be polished for reflecting all light carried within the fiber, often referred to as “the TIR angle”, is the angle complementary to the critical angle for the zeroth order ray (46.7 degrees, from above), minus the maximum propagated angle of 9.6, or just over 37 degrees (at 587.6 nm). This result is remarkably consistent across surgically relevant wavelengths (although some designers apparently assume 0.22 for a maximum NA and some designers appear to establish a nominal TIR angle that is a degree or two below the calculated maximum to account for manufacturing variability, etc.) yielding the oft cited range of lateral outputs of 70-80 degrees with respect to the fiber axis.
It bears noting that the maximum divergence of a conventional side firing fiber (akin to that depicted in FIG. 1) is not defined the same way as it is in an axial delivery fiber (through the fiber NA and the refractive index of the working medium) because side fire divergence is also a function of the fiber cladding to core diameter ratio (CCDR), the dimensions of the protective capsule (also known simply as “the cap”), the lateral output angle, the fiber position within the cap, cap geometry and other variables. The output spot of conventional side fire fibers is fundamentally elliptical—albeit an ellipse that is so highly distorted as to be unrecognizable—due to the cylindrical curvatures of the fiber outer diameter, the curvature of the cap wall through which lateral emission passes and the non-orthogonality of the output; fast and slow axes of divergence emerge and correspond to the major and minor diameters of the generally elliptical output spot.
No standards exist for characterizing side fire fiber performance. While most manufacturers do roughly specify the output angle for their fibers, they remain silent on the efficiency of turning the light in the desired direction. Additional parameters such as the irradiance (W/m2) of the spot and radiant intensity (W/sr) of the beam—with efficiency, critical parameters that describe the performance of side fire fibers in all conceivable applications—neither prior art disclosures nor company marketing materials for side fire fibers describe divergence, efficiency or the output beam profile (with American Medical Systems' MoXy™ fiber a notable exception).
Atypical lateral delivery fibers operate at 80-90 degrees, and beyond, by utilizing on-fiber numerical aperture (NA) reduction strategies and/or reflectors less influenced by incident angles, e.g. metals mirrors. The former strategy reduces divergence, increasing radiant intensity, while the latter strategy tends to extend the optical path traversed by the diverging light, reducing irradiance at the target.
A design strategy that increases both irradiance and radiant intensity is described as “fused output” fibers, where the output surface of TIR bevel-tipped fibers is joined to the inner surface of the output cap, eliminating the higher intensity reflections and refractive distortion caused by these highly curved surfaces. During surgery, however, the lateral redirecting tips of fibers are subjected to cycles of rapid heating and cooling as well as sustained and extreme heating. Thermal cycling can exacerbate stresses that are captured within fiber tips and induce fracturing about those stress concentrations, particularly in fused output fiber caps that harbor greater stress from manufacturing, i.e. the external cap cannot been annealed following highly localized melt processing, as is the case in U.S. Pat. No. 5,537,499 (Brekke), U.S. Pat. No. 5,562,657 (Griffin), U.S. Pat. No. 6,687,436 (Griffin), U.S. Pat. No. 8,073,297 (Griffin) and U.S. Pat. No. 7,463,801 (Brekke and Brucker). Transient and sustained high temperatures, at or about the transmitting surface of the cap, also accelerate the endothermic absorption of alkali metal ions within the amorphous silica matrix that forms most caps, lowering the glass viscosity sufficiently to permit rearrangement of the glassy state into thermodynamically favored crystalline states; side fire caps are susceptible to devitrification.
Metallic reflector fibers such as described in U.S. Pat. No. 5,437,660 (Johnson, et al.) may be configured to emit orthogonal radiation, but the reflectors become contaminated with tissue fragments and rapidly degrade. Fiber bevel surfaces coated with metals and multilayer dielectric coatings have been proposed for augmenting or replacing the total internal reflection (TIR) function of the bevel tip, theoretically enabling orthogonal output, e.g. U.S. Pat. No. 8,425,500 (Hanley, et al.), but such coatings have proven difficult to apply uniformly enough to survive the intense laser irradiation used in surgery.
Thermal expansion induced stresses in the side fire optical devices often result in the cap cracking or shattering. Highly localized and intense devitrification causes perforations through protective cap walls with the consequent loss of the refractive index conditions required for total internal reflection. Thermally mediated failure modes are particularly problematic where newer surgical lasers are utilized. Modern lasers produce significantly higher average powers than those of just a decade past, e.g. 120 W holmium laser energy (2080 nm to 2140 nm), 180 W “Greenlight” laser energy (532 nm), up to 250 W diode laser energy (800 nm to 1500 nm), 200 W thulium (2000 nm), and are particularly problematic when side fire fiber devices directly contact tissues during surgery.
Lateral delivery optical fibers for surgery have been described and produced for decades. Early lateral delivery fibers (FIG. 1) were simple in construction: an optical fiber 5 polished at an off-axis angle 35, between 35 and 40 degrees, about which a closed end 40 transparent tube 45, akin to a tiny test tube, is affixed (the tube is often referred to as a “protective capsule” or simply “cap”, and the surface through which the light exits is referred to as the “transmissive surface”). Deficiencies with this simple design were quickly recognized and strategies were proposed for mitigation of at least some of the recognized deficiencies; in implementation, most such strategies had little success.
The example in FIG. 1 illustrates an embodiment (U.S. Pat. No. 4,740,047, Abe, et al.) where the original cylindrically curved transmissive surface of the cap, and the cap surface 180 degrees opposing the transmissive surface, are modified to planar surfaces and coated with anti-reflection 20 and reflection coatings 30, respectively. Abe also teaches a third coating 25, a reflector for blocking axial emission, even while teaching away from a 45 degree TIR bevel, which itself is the principal source of such axial emission.
It is apparent that Abe did not fully comprehend the sources of the undesirable emissions that he sought to eliminate, particularly the axial emission due to exceeding the critical angle (for the higher angle modes in the fiber) in using a 45 degree bevel angle. In teaching away from 45 degrees, in favor of 35 degrees to 40 degrees, Abe rationale is for improved visualization of the projected beam and better scope deflection control rather than elimination of axial leakage. If functioning perfectly, the anti-reflection coating 20 Abe proposed to deposit upon the transmissive surface of the cap has very little effect on the rearward reflections (20% portion in FIG. 2A) in that the bulk of these reflections are produced (as depicted in FIG. 2B and in order of contribution to the total): (a) substantially total reflections of extremely acute angles of incidence to the fiber cladding 60 outer diameter curvature, for rays such as D (a skew ray) and C (a meridional ray) at the periphery of the fiber core 50, as taught in U.S. Pat. No. 5,428,699 (Pon), (b) FIG. 1 Fresnel reflections from light transitioning from the fiber 5 into the air gap 10 and from the air gap 10 into the protective cap wall 15 and lastly (c) the Fresnel reflections from the light transitioning from the cap wall 15 into the saline-filled working environment that Abe attempts to mitigate with the antireflective coating 20. Approximately 28% of the light exiting fibers such as taught by Abe (less the antireflective coatings) exits in directions that are surgically useless, contributing to the heating of the fiber tip and may damage non-target tissues during surgery; Abe's anti-reflection coatings reduce these reflections by less than 4%, at best (assuming operation in air).
Although the invention taught by Abe may have been sufficient to avoid damaging non-targeted tissues at the time, owing to the relatively lower laser powers used, the reflective coating 30 taught by Abe for the opposite surface of the cap has minimal effect in preventing such damage owing to the relatively narrow and central portion of the widely spread reverse output that is addressed by the coating (FIG. 2A). As illustrated in FIG. 2B, some rays of light imparting the curved side of an optical fiber, after reflecting from the bevel surface, next encounter cladding:air boundary angles at or near the critical angle for total reflection as defined by Snell's Law, e.g. rays C and D, such that a significant portion of the energy does not exit the fiber in the desired direction, but undergoes complex reflections within the tip instead, eventually exiting in a variety of directions (represented by Ct and Dt) substantially opposite of the desired direction. Low mode angle rays such as A and B with higher incident angles at the cladding:air interface refract in the general direction that is desired (At and Bt), but as the incident angles become lower B, the portion of the energy reflected increases as the portion refracted (exiting) decreases. Partial reflections Bf may be split again, with some of the energy refracting out of the fiber Bft while some is again reflected Bff back into the fiber. In short, the optical model of a standard side fire fiber tip is extremely complex and gives rise to the highly distorted emission that is a well-known characteristic of such devices.
Additional refractions and reflections occur at the air 10 to cap glass 15 interface in FIG. 1 and more refractions and reflections occur at the transmissive surface of the device, although the latter are muted due to the closer match in refractive indices between glass and irrigation fluid in surgery. Minor contributions to the overall scattering (output in directions other than the intended output) result from Fresnel reflections at the fiber core to cladding interface and additional distortion of the output results from the non-orthogonal, off axis angle of emission. In total roughly 28% (the sum of 4%+4%+20%, FIG. 2A) of the energy imparting the fiber bevel exits at angles that are not only surgically useless but actually harm the fiber and may damage non-targeted tissues. Rather than a round spot that diverges symmetrically, the classical side fire fiber output spot is typically reminiscent of a crab with a generally ovoid center (crab body) and radiating streaks (legs) where divergence is highly asymmetric and unpredictable.
Pon describes a more elegant partial solution to the problem of unwanted reflections within the standard side fire fiber output; Pon increases the cladding thickness of the fiber to reduce the amount of light imparting the fiber cylindrical wall at angles acute enough for total reflection. An embodiment of the fiber device described in Pon (Laserscope's ADD-Stat for pre-1999 lasers and Model 2090 for the GreenLight™ lasers that followed) was highly successful in the marketplace with over one million units sold in spite of expense of a disposable device based upon very expensive 1.4 CCDR (Cladding to Core Diameter Ratio) fiber: US$750 each.
Roughly contemporaneous with Pon, two patents (Brekke '499 and Griffin '657, FIG. 3) taught another strategy for reducing unwanted reflections in side firing fibers: fusion of surfaces within the optical output path. In eliminating large differences in refractive indices within the output path, the unwanted critical angle reflections (referred to as “Snell reflections” hereafter, to distinguish them from Fresnel reflections) are essentially eliminated, as are the larger Fresnel reflections and much of the cylindrical distortion of the output. Essentially no back reflections exist for the inventions as described and the output profiles are essentially oval with the relatively the relatively sharp edges typical of standard, axial fiber output profiles. Both inventions describe embodiments that may be produced with far lower cost fiber optic materials than required by Pon (e.g. 1.1 CCDR and 1.05 CCDR fiber) but both inventions also suffer a common flaw: extremely high residual stresses due to the inhomogeneous heating required to achieve fusion without damaging the polymer cladding 75 (also known as “secondary cladding”) and the fiber buffer 80 (also known as the fiber “jacket”).
As taught by Griffin '657, the fiber core 50 and cladding 60 (analogous to the core and cladding depicted in FIG. 2) is ‘overclad’ for a short segment near a terminus with a hollow cylinder of fused silica 55, the cylinder inner diameter being fused to the fiber cladding 60 outer diameter. A TIR bevel is formed at 38 degrees relative to the fiber longitudinal axis and the beveled terminus of the fiber is then fused within a closed hollow cylinder of fused silica or protective capsule 65, akin to a test tube, upon the outer diameter of the overcladding sleeve. Finally, like a portion of the art described by Abe, the cylindrical outer diameter of the protective capsule 65 is equipped with a flat 70 to serve as the transmitting surface. This construct harbors high residual stresses that are ‘frozen’ within the assembly and cannot be removed by annealing for the same reason the fusion heat was applied locally to the regions of fusion; fiber secondary cladding 75 and buffer 80 are heat labile polymers.
The inability to relieve stresses imparted to the fiber termination due to significant and localized differences in thermal history is not the sole problem with on-fiber fusion designs. Defect-free fusions are best carried out slowly such that organic contaminants harbored in the interstices have time to combust and escape before fusion initiates; rapid fusion traps gas bubbles and fusion voids as well as carbonized material. While fused quartz and fused silica have low thermal conductivity, the components are also very small, being limited in diameter and length by the endoscopic working channels (also known as the “forceps channel”) through which the devices must pass, e.g. a 6 French forceps channel is typical for flexible ureteroscopes. Heat applied for fusion is quickly conducted to the portion of the protective capsule adjacent to, and/or surrounding, the thermally labile materials.
As such, the heat for fusion is typically applied with a CO2 laser and must be completed in seconds. For example, the rounded terminus (at right, or proximal) of the overclad sleeve 55 is separated by approximately 2 mm from the secondary cladding 75 and approximately 3 mm from the ETFE buffer 80, materials which are also housed within the inner diameter of the protective capsule 65 (in this case having an outer diameter of 1.75 mm and an inner diameter of 1.2 mm.
It is advantageous for surgical performance to produce lateral output fibers that produce undistorted output spot profiles with clearly defined edges and minimal divergence. U.S. Pat. No. 6,687,436 (Griffin) is another fused side fire fiber design, similar to Griffin '657, where the output of the fiber is essentially orthogonal to the fiber longitudinal axis, afforded by reducing the maximum angular mode guided within the fiber by way of tapering the fiber to a larger diameter over a fixed length that is just proximal to the beveled tip. Output at or near 90 degrees is desirable for minimal elliptical distortion in the output spot with higher and more uniform energy density distribution within the spot: an advantage all applications, including ordinance ignition and spectroscopy.
FIG. 4 depicts Griffin '436, an orthogonal output side fire device produced from standard 0.22 NA fiber, with a protective cap 65 about a core 50, cladding 60, secondary cladding 75 and buffer 80 that are analogous to those depicted in FIG. 3. The fiber is up-tapered 85 at one end to approximately 3-fold the original fiber diameter with the goal of reducing the highest angle light energy within the fiber from approximately 8.5 degrees (@0.22 NA) to approximately 3 degrees. The distal tip about the bevel is fused 90 within the cap 65, putting the center of the output (small head arrows) at approximately 88 degrees relative to the fiber longitudinal axis with approximately ⅓rd the divergence of the device depicted in FIG. 3 (small head arrows).
The device disclosed in Griffin '436 has the same problems with residual stresses as other fused output type devices, and it shares problems with Brekke '499: the fusion portion 90 ends with an extremely acute angle about the tapered fiber 85 (Brekke is a spot fusion directly between the fiber cladding at the bevel and the protective cap so the acute angle surrounds the Brekke fusion) and the initially optically flat bevel face becomes distorted with the application of the heat for fusion. Such acute angles concentrate stresses and are commonly the originating points for fractures. A further problem in surgical applications of the device depicted in FIG. 4 is that the taper is necessarily made short in order to fit within the dimensional constraints for passing a flexible ureteroscope forceps channel such that the conversion of higher order modes to lower order modes is incomplete (required for efficient redirection of the energy at the TIR bevel), resulting in some axial leakage of energy that exceeds the maximum angle of incidence for total internal reflection.
The stresses harbored within un-annealed fused fiber designs were problematic at average power settings for surgical lasers in use for prostate vaporization a decade ago, where repeatedly and rapidly heating and cooling the side firing fiber caps amplified preexisting stresses and/or flaws, often causing fractures at the junctions of fused and un-fused portions of the assemblies. Modern surgical lasers can deliver more than twice the average power of the former installed base, making the control of Snell and Fresnel reflections even more important and rendering inviable the solutions taught in '499, '657, '436 and even '699.
The device disclosed in Griffin '297, FIG. 5, is a side fire optical device for laterally redirecting electromagnetic radiation-comprising: a cap member 100 comprising a closed end section 105, a tube section having a bore 110, and a transmitting surface 115; a sleeve 120 received within the bore of the tube section, the sleeve including a bore 125 and an exterior surface 130 that is fused to a surface of the bore 110 of the cap member 100; and a fiber optic segment comprising a core 140 and an exterior surface of fluorine-doped cladding 145, the cladding fused to a surface of the bore 125 of the sleeve 120, a beveled end surface 150 formed upon the fused fiber optic and sleeve segment and positioned adjacent the transmitting surface 115 of the cap member 100 and a (chamfered) fiber conduit receiving end 155 opposite the beveled end surface 150 that is within the bore of the outer tube section 110, wherein the beveled end surface 150 is angled relative to a longitudinal axis of the fiber optic segment 140/145 such that electromagnetic radiation propagating along the longitudinal axis of the fiber optic segment 140/145 is reflected by the beveled end surface 150 at an angle that is transverse to the longitudinal axis and through the transmitting surface 115 of the cap member 110 and variations thereof. A convex lens surface 135 may or may not be formed upon the fiber optic segment 140/145. This invention solves the problem of post-fusion annealing in that the fused side firing mechanism is accomplished entirely within a separate glass structure that may be annealed prior to coupling to the transmitting optical fiber conduit, while also essentially eliminating Snell reflections and greatly reducing Fresnel reflections. Minor Fresnel reflections remain due to the lower refractive index of the fiber optic segment cladding 120 relative to the fiber optic segment core 140 and the sleeve 130 and at the fused surfaces (due to contamination, captured gases, differential surface chemistry, etc.) but close examination of the invention described in '297 reveals numerous shortcomings.
Most of the claimed functions taught in '297 are illusory beyond the physical separation of the cap (and lateral turning elements) from the transmitting optical fiber conduit (thermally labile materials). In brief, the utility of the sleeve 120 that is fused about the fiber optic segment 140/145 is taught to be for aligning the fiber optic conduit (core and cladding within bore 125, secondary cladding and buffer within bore 110) and for displacing the TIR surface 150 from the heat used for fusing the fiber segment 140/145 and sleeve 120 into the cap 100, reducing fusion associated distortion of the TIR surface. A concomitant result of using the sleeve over the fiber is an extension of the optical path, addition of a new fusion surface (where no fusion surface is perfect) and minimization of the optical aperture of the lens 135 produced on the fiber optic segment 140. Adding the sleeve to the design also reduces the thickness of the protective cap 100, rendering the device more fragile and more easily perforated by devitrification.
The use of fiber optic material for the segment 140/145 renders the segment length immaterial, easing assembly, yet also renders the lens 135 without function unless the mated optical fiber conduit is of substantially smaller core than the fiber optic segment 140/145 and the segment itself is shorter than twice the effective focal length of the lens 135, least some of the ‘focused’ energy leak through the cladding 145. Further, the fluorine dopant in the fiber optic segment 140 cladding may diffuse into the sleeve 120 and cap 100 during annealing, and during surgical heating, predisposing the glass cap to devitrification. Additional deficiencies exist where compared to later designs, such as those taught in U.S. patent application Ser. No. 14/578,739 (Griffin)—filed Dec. 22, 2014, the disclosure of which is incorporated herein in its entirety—and the art taught herein.
It would be useful and novel to provide a means for minimizing potential Fresnel reflections, even those resulting from the relatively similar refractive indices of fiber cladding 145 and fiber core 140 materials at fused surfaces, and for eliminating Snell and Fresnel reflections, within a self-contained lateral output assembly (within which a transmitting optical fiber conduit may be subsequently attached) that enables a truly orthogonal output (relative to the fiber longitudinal axis) with divergence similar to, or lower than, that of the transmitting optical fiber conduit. Griffin '739 teaches remedies for the failings of '297 that meets many of these challenges.
FIG. 6 is a preferred embodiment taught in '739, wherein a quartz or silica rod is rounded to a convex lens 180 on one end and a bevel is machined on the opposite end 175. The shaped rod 160 is fused within a tube of like material 165 that is closed on one end 170, comprising a lateral delivery capsule. The invention becomes a very high efficiency lateral delivery device upon introducing an optical fiber 215 through the open end 185 of the closed tube. The fiber is centered within the lateral delivery capsule via a sleeve 190 about the outer buffer 195. The delivery tip of the fiber 205, comprised of the fiber core 210 and fluorine-doped cladding 205, is denuded of polymer cladding 200 and buffer 195 in the immediate vicinity of the output 210. The opposite end of the fiber 215 (not shown) is connected to a laser source and delivers the laser energy to the lens element 180, where the light is partially collimated or focused before imparting the TIR bevel 175 for redirection off the fiber longitudinal axis.
The embodiment of '739 described above and depicted in FIG. 6, where the lateral delivery capsule outer diameter is 2.2 mm, is compatible with 7 French bore forceps channels within the cystoscopes used for accessing the prostate gland. The optical fiber is a standard 0.22 NA, 1.1 CCDR, 0.6 mm silica core fiber and is centered within the 1.4 mm bore of the lateral delivery capsule and fixed in position with adhesive. Fresnel reflections from the fiber core to the air gap 220 transition are coupled back into the fiber core 210 toward the laser source. The Fresnel reflections from the air 220 to convex lens surface 180 are directed generally toward the open end of the capsule, but in a highly divergent solid cone such that very little of this energy imparts laser labile materials such as the fiber secondary cladding 200, buffer 195 and adhesive. Testing in an aqueous environment produced no thermal damage to the fiber buffer or secondary cladding at 200 watts average power for 15 minutes (980 nm, CW).
Approximately 100% of the energy that enters the shaped rod 160 through the lens 180 is redirected laterally through the transmitting surface 225 of the capsule 165 where the final refractive index transition—capsule to saline irrigation fluid—produces a small Fresnel reflection. Tests of this device under surgical conditions (150 W, CW at 2000 nm in non-contact vaporization of tissue), have failed to expose any propensity for typical side fire fiber failure modes at and beyond 200 kilojoules of total energy applied: in excess of the energy required for many surgical applications. Use for vaporization of tissue in direct contact and above 120 watts average power (2000 nm) does produce devitrification damage but the point at which degradation of performance begins has yet to be determined.
The approximately 75 degree (central) output angle (relative to the fiber longitudinal axis) exhibits perpendicular divergence of approximately 12 degrees and parallel divergence of approximately 6 degrees, in air, as compared to the highest performance side fire fiber currently marketed at 15 degrees and 7 degrees, respectively (MoXy™ specifications per American Medical Systems literature).
U.S. patent application Ser. No. 14/020,289 (Griffin, et al.), filed Sep. 6, 2013 teaches the art enabling the MoXy fiber: a low divergence, high power lateral fiber that utilizes coaxial water cooling. Referring to FIG. 3, MoXy is essentially a hybrid of Griffin '657 and a modified, but relatively conventional side fire fiber. A capsule 65, having a very thin wall, is fused directly about a bevel tipped fiber 50 and sealed like a test tube about the bevel tip to preserve the refractive index needed for total internal reflection; the sleeve 55 is omitted. This delicate side fire fiber is then enclosed within a robust capsule, much as a conventional bevel tipped fiber is enclosed within a conventional side fire fiber capsule 45 as depicted in FIG. 1. Griffin '289 deviates from convention in failing to completely seal the outer capsule at the distal end, leaving a port for communicating fluid from within the capsule to outside of the capsule, at or about the location between the arrows at 25 and 40. The opposing, open end of the outer capsule is affixed to a cannula having a lumen for communicating fluid to the capsule under pressure or gravity flow. The bevel tipped fiber, sealed within the thin wall inner capsule, is centered within the larger, outer protective capsule such that fluid delivered to the capsule (by way of the cannula) forms an annular cooling jacket about the inner capsule and exits the hole in the traditionally sealed capsule at the distal terminus.
By filling the space between the inner capsule and the outer capsule with saline, the Fresnel reflections and the cylindrical distortion plaguing conventional side fire fibers are greatly reduced. Residual stress resulting from fusion of the thin wall inner capsule about the bevel tipped fiber is reduced by using the very thin cylinder and the inner capsule is shielded from thermal cycling by the outer capsule and the continuous coolant fluid flow, greatly reducing the risk of fracture from thermal cycling about internal stresses. The fluid flow also cools the outer protective capsule from within, largely preventing it from rising to temperatures sufficient to initiate tissue adhesion and devitrification. The MoXy fiber operates at 180 W, quasi-CW at 532 nm and performs exceptionally well through 650 KJ of total applied energy.
Side fire fibers that are currently available to surgeons are exclusively single use—they are discarded post-operatively with disposable device costs ranging from approximately $500 (Lumenis DuoTome) to more than US $1000 each (MoXy). High performance fibers like MoXy are competent for completing surgeries on the largest of prostate glands, even in cases where a patient has been taking drugs such as Flomax for years and/or the patient has had a prior treatment by laser (VLAP, PVP, HoLAP), microwave (TUNA) or electrocautery device (TURP). More than one fiber is commonly needed to complete such cases where lesser performance fibers are utilized.
The fiber optic conduit and laser connector represent roughly 80% of the materials costs for producing a classical side fire fiber, and between 50% and 70% of the labor costs are directed toward producing the distal termination (side fire tip), particularly in forming the TIR bevel on the fiber. Although a great deal of the higher cost of the MoXy fiber is due to the use of a larger fiber than is usual (0.75 mm core), much of the cost is also due to the expense of providing the coaxial cooling to the double cap design. It would be useful and novel to provide a side fire fiber capable of being used in multiple surgical sessions through interoperative reprocessing or where the protective cap may be replaced interoperatively (and perhaps even intraoperatively). It would be useful and novel to provide a high performance side fire fiber at far lower cost than MoXy by eliminating the need for coaxial cooling and on-fiber production of TIR bevels.